Many photoinitiators have been developed which are soluble in, and effectively cure, unsaturated organic resins. However, it has been found that such photoinitiators often have limited solubility, and therefore reduced curing effectiveness, in silicones. To overcome this compatibility problem, it has been proposed chemically bond certain photoinitiating moieties to silicones.
A Japanese patent publication, Kokai No. 34,291/76 describes the use of benzophenone derivatives, such as 4-dimethylamino-4'-(trimethoxysilylbenzophenone, in preparing the silicone compatible photoinitiators.
Another Japanese patent publication, Kokai No. 71,199/78, describes the preparation of photoinitiators from the reaction of alkenylsilylbenzophenone and silicones containing silicon hydrides.
Japanese patent publication Kokai No. 50,067/79 and U.S. Pat. No. 4,273,907, describe benzoin type photoinitiators attached to the ends of polydimethylsiloxane through an Si--O--C bond. However, the Si--O--C bond is well known to be hydrolytically unstable.
In U.S. Pat. No. 4,391,963 and in co-pending application Ser. No. 505,588, filed June 20, 1983, there are described silicones having benzoin photomoieties bonded thereto through Si--C bonds. These materials are prepared by hydrosilation of alkenyl substituted benzoins.
In co-pending application Ser. No. 528,287, filed Aug. 31, 1983, there are described Si--H functional siloxy compounds having various alkyl-aryl ketone photoinitiating moieties bound to silicon. These compounds are also prepared by hydrosilation of appropriate olefinically or acetylenically unsaturated photomoieties.